:root {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --text-primary: #e2e8f0;
    --text-secondary: #94a3b8;
    --accent-cyan: #06b6d4;
    --accent-purple: #8b5cf6;
    --glass-bg: rgba(30, 41, 59, 0.7);
    --glass-border: rgba(255, 255, 255, 0.1);
}

* {
    box-sizing: border-box;
    scroll-behavior: smooth;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.8;
    overflow-x: hidden;
}

/* Typography */
h1, h2, h3 {
    font-weight: 800;
    letter-spacing: -0.05em;
    margin-bottom: 1rem;
    color: #fff;
}

h1 {
    font-size: 3rem;
    background: linear-gradient(to right, var(--accent-cyan), var(--accent-purple));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

h2 {
    font-size: 2rem;
    border-bottom: 2px solid var(--accent-purple);
    padding-bottom: 0.5rem;
    margin-top: 3rem;
}

p, li {
    font-size: 1.1rem;
    margin-bottom: 1.2rem;
    color: var(--text-secondary);
}

strong {
    color: var(--accent-cyan);
}

/* Layout */
.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 2rem;
}

/* Header */
header {
    height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    background: radial-gradient(circle at 50% 50%, #1e1b4b 0%, var(--bg-primary) 100%);
}

.hero-btn {
    margin-top: 2rem;
    padding: 1rem 2rem;
    background: linear-gradient(45deg, var(--accent-cyan), var(--accent-purple));
    color: white;
    font-weight: bold;
    border-radius: 50px;
    text-decoration: none;
    transition: transform 0.3s, box-shadow 0.3s;
}

.hero-btn:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 20px rgba(139, 92, 246, 0.5);
}

/* Sections */
section {
    padding: 4rem 2rem;
    margin: 2rem 0;
    background: var(--bg-secondary);
    border-radius: 20px;
    border: 1px solid var(--glass-border);
    box-shadow: 0 4px 30px rgba(0, 0, 0, 0.5);
}

/* Images */
.concept-image {
    width: 100%;
    border-radius: 12px;
    margin: 2rem 0;
    box-shadow: 0 0 20px rgba(6, 182, 212, 0.3);
    transition: transform 0.5s;
}

.concept-image:hover {
    transform: scale(1.02);
}

/* Code Blocks */
pre {
    background: #000;
    padding: 1.5rem;
    border-radius: 8px;
    overflow-x: auto;
    border: 1px solid var(--accent-purple);
    color: #a5f3fc;
}

code {
    font-family: 'Fira Code', monospace;
}

/* Quiz */
.quiz-box {
    background: rgba(0, 0, 0, 0.3);
    padding: 1.5rem;
    border-radius: 12px;
    margin: 2rem 0;
    border-left: 4px solid var(--accent-cyan);
}

.quiz-question {
    font-weight: bold;
    margin-bottom: 1rem;
    font-size: 1.2rem;
}

.options button {
    display: block;
    width: 100%;
    text-align: left;
    padding: 1rem;
    margin: 0.5rem 0;
    background: var(--bg-primary);
    border: 1px solid var(--glass-border);
    color: var(--text-secondary);
    border-radius: 8px;
    cursor: pointer;
    transition: 0.3s;
}

.options button:hover {
    background: rgba(6, 182, 212, 0.1);
    border-color: var(--accent-cyan);
    color: white;
}

.quiz-answer {
    margin-top: 1rem;
    padding: 1rem;
    background: rgba(6, 182, 212, 0.2);
    border-radius: 8px;
    display: none; /* Hidden by default */
    color: #fff;
}

.quiz-answer.visible {
    display: block;
    animation: fadeIn 0.5s;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Footer */
footer {
    text-align: center;
    padding: 4rem;
    color: var(--text-secondary);
    border-top: 1px solid var(--glass-border);
}